The present invention relates to a method of manufacturing a sample for an atom probe analysis by an FIB, and an apparatus capable of easily implementing that method.
As means capable of directly observing an atomic arrangement of a needle point, there is developed an atom probe (AP: Atom Probe) that is a composite instrument of a mass spectrometer capable of detecting a single ion and a field-ion microscope (FIM). The AP is a solitary device capable of analyzing an electronic state, the atomic arrangement and a composition distribution of the needle point. Since a field evaporation orderly proceeds in every atom layer from a surface first layer, by the AP it is possible to investigate a composition or the composition distribution of an interface, and additionally an electronic state change in every layer. However, for this AP, there is a strict restriction in a manufacture and a shape of a sample, so that a field in which its characteristic can be practically used is limited. One devised in order to break down this restriction is a scanning atom probe (SAP: Scanning Atom Probe). In order to select a specified needle from needles densely arranged and investigate its tip, an electric field must be localized to the needle point. Whereupon, a grounded fine funnel type leader electrode is attached to an inside of a housing of the AP, and a positive voltage is applied to a planar sample in which fine needles are densely arranged. Thereupon, a high electric potential generates in a single needle point existing just below a hole, whose diameter is several μm to several tens μm, in a tip of the leader electrode, and the electric field is localized to a very narrow space between the hole and the needle point. According to an electric field distribution calculation by a computer, even if an apex angle of the needle point is 90° and a tip curvature radius is 50 nm, in the needle point there is generated the high electric field demanded in an electric field radiation and the field evaporation. This fact shows the fact that, if a concave/convex of about several μm exists on a flat sample face, it is possible to analyze a tip of its protrusion. Since a surface to which there is applied no flattening processing, a corroded surface, a surface of highly efficient catalyst, and the like are normally rich in the concave/convex, it follows that these surfaces are investigates as they are. In FIG. 7, there is shown a basic structure of the SAP. A sample S in a left end is one showing schematically a densely arranged type electric field radiation electron source. If a hole in a tip of a funnel type leader electrode TE approaches to a tip of the needle point or the protrusion on the sample face, the high electric potential generates in a very narrow region between the tip and the electrode, and electrons radiated from the needle point project an FEM image to a screen SN. Further, if an inert image gas such as helium is introduced into the housing and the positive voltage is applied to the sample S, an FIM image of a high resolving power is projected to the screen SN. Additionally, if a surface atom is field-evaporated by superimposing a pulse voltage onto a steady-state voltage or irradiating a pulse laser light PL to the sample face, the surface atom evaporated as a positive ion enters into a reflectron REF that is the mass spectrometer while passing through an exploration hole in a center of the screen SN, and is detected one by one. A region to be analyzed is a region, whose diameter is several nanos to several tens nanos, of a protrusion tip corresponding to the exploration hole. If the analysis is continued, it is possible to investigate a composition change in a depth direction of this region with a resolving power of one atom layer.
If the sample having in its surface the concave/convex, especially a convex portion, is found, it is opposed to the leader electrode, the sample protrusion part is field-evaporated in order from an upper layer atom, and it is drawn out as the ion and detected by an ion detector (two-dimensional detection type) disposed rearward the leader electrode, since an element analysis is possible by a time-of-flight measurement of each ion and also a position information is obtained, a three-dimensional composition analysis in an atomic level is possible. In a case where an analysis object sample of a semiconductor wafer, a thin film magnetic head wafer called GMR or TMR, for which there are strong needs, or the like is made the sample, it is frequent that it becomes a multi-layered structure in which complicated patterns are overlapped, and a structure of a portion desired to be analyzed is various. In order to analyze the analysis object like this by using the AP, although it is necessary to locally cut out a place desired to be analyzed and fix it to a tip of a needle-like protrusion becoming an electrode while being cut out as a fine section, hitherto there merely exists only a conventional method of making a sample of metal material or the like into needle-like one, so that it is very difficult to analyze a fine specified site by the AP. Therefore, as a technique replaceable with this, a development in a preliminary working technique working the sample itself like the needle becomes indispensable. With a relation that it is the analysis in the atomic level, since an analysis object dimension becomes about 100 cubic nm, a technique for manufacturing a analysis object part to a needle-like sample in a pinpoint becomes very important.
As one responding to such needs, the present inventor previously presented JP-A-2005-265516 Gazette entitled “Atom probe apparatus and its sample preliminarily working method”, published on Sep. 29, 2005. Problems of this invention are to present a technique of a sample preliminarily working in which a place desired to be analyzed of a device is locally cut out to thereby be made a needle-like protrusion, and to present a technique in which, even if it is a sample of a multi-layered structure including an atom layer of a small evaporation electric field in a certain circumstance, an orderly stable ion evaporation is made possible, thereby making an SAP analysis in the atomic level possible. And, the preliminary working of the sample for the atom probe apparatus of this invention comprises a step of cutting out, like a block, a sample desired observation site by using a focused ion beam (FIB) apparatus, a step of temporarily bonding the cut-out block-like sample by an FIB-CVD, a step of making a notch over a base part of the block-like sample and a sample substrate by an FIB etching, a step of bonding/fixing the sample substrate and the block-like sample by applying thereafter the FIB-CVD to the notched portion, and a step of working the block-like sample fixed on the sample substrate into a needle point shape by an FIB etching working. Further, the sample worked into the needle point shape is one worked such that a layer direction in the multi-layered structure becomes parallel to a longitudinal direction of a needle.
As to an AP sample needle, since it is necessary to concentrate an electric field to the tip, although it is necessary to transplant a sample piece onto a base metal needle or a base Si circular cone pillar, one making it possible is a sample piece picking/transplanting technique by the above FIB. This technique is one in which a transmission electron microscope (TEM) sample thin piece manufacturing technique is applied. However, in this sample piece picking/transplanting technique, there is the fact that there generates such an issue that, by a strong electrostatic attraction force at an AP analysis time, a transplantation piece in a front from a joint part flies and is lost. This issue is one generating because a strength of an interface between a deposition film and a material to be bonded, which are bonded by the FIB-CVD, is insufficient and they are exfoliated.
A problem of the invention is to solve the above issue, i.e., to present, in a transplanting/bonding method of an atom probe sample piece, a firm bonding/fixing technique of the sample substrate and the block-like sample, which can sufficiently withstand the strong electrostatic attraction force at the AP analysis time.